1. Field of the Invention
The present invention relates to an endless metal belt, a fixing belt and a heat fixing device (or assembly), which are used in image-forming apparatuses such as an electrophotographic apparatus and an electrostatic recording apparatus.
2. Related Background Art
In an image-forming process such as an electrophotographic process, an electrostatic recording process and a magnetic recording process, a heat fixing device (or assembly) of a belt-heating system is used for forming a permanently fixed image on the surface of a recording material from an unfixed image (a toner image) which is formed on and carried by a recording material (a transfer material sheet, an electrofax sheet, electrostatic recording paper, an OHP sheet, printing paper, format paper and the like), by means of a transfer method or a direct method.
On the other hand, as a heat fixing device of a belt-heating system, a heater heating type is widely proposed and implemented which heats a resin belt or a metal belt having a low heat capacity using a ceramic heater as a heat source. Specifically, the heat fixing device of a belt-heating system of a heat-heating type generally has a nip part formed between a ceramic heater as a heating body and a pressure roller as a pressure member through a heat resistant belt (a fixing belt); makes a recording material having an unfixed toner image carried thereon introduced between the fixing belt and the pressure roller; while sandwiching the recording material between the fixing belt and the pressure roller, and transporting it along with the fixing belt, gives the heat of the ceramic heater to the recording material through the fixing belt in the nip part; and heat-fixes the unfixed toner image on the recording material with the heat and an applied pressure in the nip part.
The heat fixing device of a belt-heating system of a heater heating type can constitute an on-demand type device by using a member with a low heat capacity for the fixing belt. Specifically, the fixing device has only to heat a ceramic heater of a heat source to a predetermined fixing temperature by applying an electric current to the heater, only when an image-forming apparatus carries out image formation, has a short waiting time after the image-forming apparatus is powered on until it comes to an image-forming ready condition (a quick starting property), and has a power consumption largely reduced during a stand-by period (capable of saving power), which are advantageous.
As for a fixing belt used in such a heat fixing device of a belt-heating system of a heater heating type, it is proposed to use a fixing belt employing a metal for the base material.
A fixing belt using a metal as a base material generally employs a seamless metal such as SUS or nickel, and a well-known seamless belt made from a SUS material is produced by a plastic forming method such as spinning (for instance, see Japanese Patent Application Laid-Open No. 2001-225134). A seamless belt made from a nickel material is generally produced by electroforming in a nickel sulfamate bath or a nickel sulfate bath (for instance, see Japanese Patent Application Laid-Open No. H09-034286 and 2001-215820).
Generally, in the present circumstances, an SUS belt made by a plastic forming method (rolling, drawing, spinning or the like) cannot cope with tendencies of a decreasing diameter (a diameter of 18 mm or smaller) for a fixing belt, and thinning (a thickness of 15 μm or less) for a base material of the fixing belt, which are required by a small-sized, high-speed and more durable fixing device. Specifically, the SUS belt has a different stress distribution in an MD direction from that in a TD direction, so that the SUS material is feared to cause cracking due to the uniaxial orientation of the axes of the crystals.
On the other hand, in an electroformed nickel belt, there has been a tendency that heat resistance has been thought much of and strength and abrasion resistance have been sacrificed. For this reason, a fixing belt produced with the use of such an electroformed nickel belt usually had a sliding layer made from polyimide provided on a sliding surface. However, because a so-called resin-based material starting with polyimide has a heat conductivity of approximately 300 times lower than that of a nickel material, a heat fixing device using such a material needs a long rise time and hides the merits of a nickel material having high heat conductivity.
An electroformed belt from a single metal hardly has the performance satisfying all demands such as yield strength, abrasion resistance and flexing resistance. For this reason, Japanese Patent Application Laid-Open No. 2002-241984 proposes a method for producing an electroformed belt containing various metallic elements in combination and having more excellent characteristics. For instance, an electroformed nickel belt is disclosed which contains 10 to 10,000 ppm (1% by weight) by weight proportion, at least one metallic element belonging to the groups of 2, 3, 4 and 5 in the periodic table. The metallic elements in the groups of 2 to 5 in the periodic table have such characteristics as to control the growth of plated nickel crystals, systematically grow the crystals and promote the orientation, have the effect of inhibiting coarsening of the plated nickel crystals due to heat, and thereby are assumed to provide the electroformed nickel belt the hardness of which hardly lowered even by heat aging and which is superior in heat resistance.
In addition, Japanese patent Application Laid-Open No. 2002-241984 discloses that when the electroformed nickel belt contains more than 10,000 ppm (1% by weight) of metallic elements in the groups of 2 to 5 in the periodic table by weight proportion, the metallic elements tend to precipitate in grain boundaries and make the electroformed nickel belt fragile.
Actually, many electroplated coatings of binary and ternary alloys are industrially widely used for machine parts and electronic components. The mechanical and electrical characteristics of the electroplated coatings of the alloys are closely connected with the composition. Furthermore, the existing state of an alloying element (such as a compound, a crystalloid and a solid solution) affects the characteristics (hardness, flexibility, stress in electrodeposits and the like) of the electroplated coatings of the alloys.
A fixing belt used in a heat fixing device must have durability for a long time. Furthermore, requirements for energy saving and space saving become severer, the miniaturization and speedup of a heat fixing device used in an image-forming apparatus, the reduction in the diameter of a fixing belt, and the thinning of a metal belt are promoted, and based on this, the metal belt having adequate abrasion resistance and superior characteristics such as flexing resistance, flexibility and durability, is demanded.
In a heat fixing device of a belt-heating system of an electromagnetic induction heating type for directly heating a metal belt by electromagnetic induction as well, the miniaturization and speedup of the heat fixing device, a reduction in the diameter of a fixing belt, and the wall-thinning of the metal belt are also promoted, and based on this, the metal belt having adequate abrasion resistance and superior characteristics in terms of flexing resistance, flexibility and durability, is demanded.